Move symmetric encryption/decryption code from leap.common to leap.soledad.
Remove strict dependency on leap.common.

* Encapsulate leap_assert and leap_assert_type so Soledad works without them.
* Remove dependency on leap.common.files.mkdir_p().
* Encapsulate signaling.
* Add changes file.
Update dependencies.
Merge remote-tracking branch 'drebs/feature/2602-remove-strict-dependency-on-leap.common-2' into develop
Remove unneeded imports from Soledad tests.
add changes file detailing initscript enhancements
Add encrypted sync test case.
Merge remote-tracking branch 'micah/feature/improve_initscript' into develop
Add changes file.
Merge remote-tracking branch 'drebs/feature/2710-add-encrypted-couch-sync-test' into develop
Do not list the backends as __all__
Make request timeouts modifiable
Merge remote-tracking branch 'remotes/chiiph/bug/modifiable_timeout' into develop
Split client and server in two different packages and refactor.
Fix couch tests so there's just one instance of couch server for each test.
Fix soledad tests so the mocked target does not influence other tests.
Add missing dependencies.
Add changes file.
Merge remote-tracking branch 'drebs/feature/2616-separate-soledad-into-client-and-server-2' into develop
Bump version and fold in changes for 0.2.1 release